Understanding the structure and properties of geological formations can reduce the cost of drilling wells for oil and gas exploration. Measurements made in a borehole (i.e., down hole measurements) are typically performed to attain this understanding, to identify the composition and distribution of material that surrounds the measurement device down hole. To obtain such measurements, a variety of sensors are used, including nuclear magnetic resonance (NMR) sensor probes. When used down hole, in conjunction with a magnet and drive electronics, measurements made by the NMR sensor probe can be used to provide information about the surrounding formation.
Generally, a permanent magnet's remnant field strength (B0) is a function of temperature. Thus, when magnets are used in locations where temperatures vary widely, such as down hole, the preferred NMR activation frequency (which gives the best signal strength) may change with temperature. Searching to locate the preferred NMR frequency at any given temperature can be time-consuming.